2017 Sales

Initial Model

For an initial pass, we constructed a model in which valid sales prices were predicted by land and improvement values. The values taken from this baseline model were then used to calculate updated assessed values.

Base Results
COD 12.986829
Ratio 1.008983

With a very basic model, we were able to achieve reasonable values on both COD and Ratio.

Existing Neighborhood Results

As a next step, we computed individual regressions for each pre-existing neighborhood with at least 5 sales.

Min = 5

Neighborhood Results
trueCOD 12.3640145
ratio 0.9852967
proportion 0.9108841

Min = 3

Neighborhood Results
trueCOD 11.6518168
ratio 0.9958052
proportion 0.9108841

New Neighborhoods (Individual Distance)

Min = 5

Neighborhood Results
trueCOD 12.1791030
ratio 0.9953730
proportion 0.9704129

Min = 3

Neighborhood Results
trueCOD 11.6267601
ratio 1.0029825
proportion 0.9704129

New Neighborhoods (Midpoint Distance)

Min = 5

Neighborhood Results
trueCOD 11.9493777
ratio 0.9956412
proportion 0.9682592

Min = 3

Neighborhood Results
trueCOD 11.4635032
ratio 1.0026736
proportion 0.9682592

School Districts

Min = 5

School District Results
trueCOD 12.966301
ratio 1.004886
proportion 1.000000

Min = 3

School District Results
trueCOD 12.966301
ratio 1.004886
proportion 1.000000

Tax Districts

Min = 5

Tax District Results
trueCOD 13.529929
ratio 1.021243
proportion 1.000000

Min = 3

Tax District Results
trueCOD 13.49978
ratio 1.02146
proportion 1.00000

Township

Min = 5

Township Results
trueCOD 13.657369
ratio 1.020274
proportion 1.000000

Min = 3

Township Results
trueCOD 13.657369
ratio 1.020274
proportion 1.000000

Tract

In an attempt to find an additional way to create neighborhoods, we also used Census Tracts.

Min = 5

Tract Results
trueCOD 13.0724675
ratio 0.9954585
proportion 0.9884304

Min = 3

Tract Results
trueCOD 13.0194347
ratio 0.9960852
proportion 0.9884304

Combined

After examining individual geographical areas, we made an effort to nest geographical features into two levels.

School District & Township

School District & Township Results
trueCOD 13.618109
ratio 1.019515
proportion 1.000000

Township & Tax District

Township & Tax District Results
trueCOD 13.529929
ratio 1.021243
proportion 1.000000

Tax District & Tract

Tax District & Tract Results
trueCOD 12.9042242
ratio 1.0035928
proportion 0.9342727

Clustering

Given the relative performance of tract, an effort was made to break the homes within tract into discreet clusters. The features selected clustering were acreage, year built, finished dwelling area and finished rooms. For each individual school district or tract, 2 distinct clusters were created.

School District Clusters

School District Cluster Results
trueCOD 13.001373
ratio 1.004109
proportion 0.993250

Tract Clusters

Tract Cluster Results
trueCOD 12.2761470
ratio 1.0036373
proportion 0.8031071

Mixed Models

Instead of fitting models to individual groupings, we also tried a mixed model in which every tract X cluster combination has its own slope within the model.

Base Results
COD 10.597028
Ratio 1.009745

Previous Years

Given the reasonable results of the tract X cluster combination, we can see how it performs over the previous years.

2016

Township Results
trueCOD 14.359149
ratio 1.041651
proportion 1.000000
Neighborhood Results
trueCOD 12.4446684
ratio 0.9859240
proportion 0.9678307
Tract Results
trueCOD 12.6581642
ratio 1.0021349
proportion 0.7999526

2015

Township Results
trueCOD 12.875449
ratio 1.018672
proportion 1.000000
Neighborhood Results
trueCOD 12.0115865
ratio 0.9807339
proportion 0.9226224
Tract Results
trueCOD 12.2462482
ratio 1.0006408
proportion 0.8021374

2014

Township Results
trueCOD 12.10949
ratio 1.02665
proportion 1.00000
Neighborhood Results
trueCOD 10.9318154
ratio 0.9910232
proportion 0.9628340
Tract Results
trueCOD 10.7454565
ratio 1.0012982
proportion 0.7861609

2013

Township Results
trueCOD 16.805726
ratio 1.028595
proportion 1.000000
Neighborhood Results
trueCOD 13.7349915
ratio 0.9935612
proportion 0.9634921
Tract Results
trueCOD 14.1780947
ratio 0.9991709
proportion 0.7949596